Using affinity purified polyclonal antibodies a 3.6kb cDNA clone of chicken nonmuscle myosin heavy chain (MHC) was isolated from a lambda gtll library of intestinal brush border. A 5' fragment of this clone was used to obtain further clones from a human lymphocyte cDNA library, which in turn, has helped to extend the chicken brush border sequence towards the 5' terminus. We have thus been able to compare these sequences of vertebrate nonmuscle MHC between species. To obtain complete sequence data on a nonmuscle MHC, we have produced new libraries, using random primers and specific oligonucleotides from our established sequence. We have also begun biochemical studies of the cloned fragments, expressing the light meromyosin encoded by our initial clone, in E. coli.